Cutting out huge swaths of users at once just stifles the content including the small percentage of actually quality content. You can't pick out and keep the good stuff when you cut off whole instances. It also brings down the engagement in your own content.

Take your favorite small forum and now split it according to political opinion, now split it again according to if users pirate movies(lol). Your forum is now dead since no one likes speaking into the void.

We should be treasuring the connections, not putting up walls because it makes the circle jerk easier.